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The destruction of aquatic ecosystems is a major issue facing conservationists globally – causes include microplastic pollution, acidification, global warming and over-fishing. The manufacturing team at NHBS have produced a series of new survey nets designed to help researchers gather data on microplastics and to sample plankton more efficiently. This blog describes the sea trials performed using our prototype nets to establish the optimal towing speeds and sea conditions as well as whether the nets worked effectively and were robust enough to withstand exposure to the marine environment.
Three new nets were tested – the Manta Trawl Net, which is designed to sample microplastics in calmer inshore waters and on rivers and lakes. The Avani Trawl Net, which is designed to sample microplastics in rougher, offshore environments and the Bongo Net (a pair of 300mm plankton nets joined in the middle and weighted with a depressor vane) which is designed to allow researchers to use two different mesh nets during a single trawl. Plymouth Sound was an ideal location, as we had both inshore and offshore designs to test and the breakwater provided us with easy access to both sheltered water and the open ocean.
The first design tested was the Bongo Net. The net performed very well. The sampling depth was easily adjusted by modulating the speed of the boat and the depressor vane kept the net level in the water. In our tests the Bongo Net performed best at towing speeds of between two and four knots.
Next, we tested our inshore Manta Trawl Net. The Manta Trawl Net is designed for microplastics sampling in calm inshore waters and on rivers and lakes. The Manta Trawl Net has a post box shaped aperture and twin ‘wings’ (manta wings) mounted onto the frame which serve to lift the net frame so that samples are efficiently collected at the top of the water column. This net was tested at a variety of towing speeds and performed best at speeds of between two and four knots.
The last net to be tested was The Avani Trawl Net. The Avani Trawl Net is designed for offshore microplastics sampling. The vertical orientation of the aperture of the net ensures that samples are collected from the top few centimetres of the water’s surface in slight to moderate swell conditions. To test this net, we ventured out beyond the breakwater where the swell was approximately 1-2m. The net stood upright and performed as expected at speeds of between four and eight knots when exposed to smaller waves of approximately one metre in height. When approaching larger waves, we found that the net had a slight tendency to cut into the side of the wave at speeds of between six and eight knots and that the net performed best at slightly lower speeds.
All of the nets functioned properly, and our haul included both microplastics and icthyoplankton (fish eggs and larvae). Both the frames and the nets also withstood the sea conditions well and we could find no faults with their design or build – all told a successful trial.
If you are interested in these nets look out for them in our 2019 catalogue, find them on nhbs.com, or contact us on firstname.lastname@example.org and we will send you more information as soon as it becomes available.